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Situation Update: Summary of Weekly FluView Report

FluView Activity Update (Key Flu Indicators)

Influenza activity in the United States continued to decrease, and is below the national baseline for the second consecutive week since late November according to the latest FluView report. Influenza-like illness (ILI) dropped from 2.1% reported last week to 1.8%. Current data indicate that the 2017-2018 flu season peaked at 7.5% in early February (during week 5). However, 5 states continue to report widespread flu activity and 1 state continues to experience high influenza-like illness (ILI) activity. Hospitalization rates this season have been record-breaking, exceeding end-of-season hospitalization rates for 2014-2015, a high severity, H3N2-predominant season. CDC also is reporting an additional 5 flu-related pediatric deaths during week 15, bringing the total number of flu-related pediatric deaths this season to 156. Sporadic flu activity is expected to continue to occur for a number of weeks. CDC recommends prompt treatment with influenza antiviral medications for people who are severely ill and people who are at high risk of serious flu complications who develop flu symptoms. Below is a summary of the key flu indicators for the week ending April 14, 2018 (week 15):

  • Influenza-like Illness Surveillance: For the week ending April 14, the proportion of people seeing their health care provider for influenza-like illness (ILI) decreased to 1.8% from 2.1%, and is below the national baseline of 2.2% for the second consecutive week since late November. However, one of 10 regions (Region 1) continue to experience a proportion of outpatient visits for ILI at or above their region-specific baseline level. ILI was been at or above the national baseline for 19 weeks this season. Over the past five seasons, ILI has remained at or above baseline for 16 weeks on average with 20 weeks being the longest.
  • Influenza-like Illness State Activity Indicator Map: Two states experienced high ILI activity (Alaska and Arizona). Two states experienced moderate ILI activity (Nebraska and Virginia). Eleven states experienced low ILI activity (Connecticut, Georgia, Hawaii, Indiana, Kentucky, Massachusetts, Michigan, North Carolina, Pennsylvania, South Carolina, and Vermont). New York City, the District of Columbia, Puerto Rico and 35 states experienced minimal ILI activity (Alabama, Arkansas, California, Colorado, Delaware, Florida, Idaho, Illinois, Iowa, Kansas, Louisiana, Maine, Maryland, Minnesota, Mississippi, Missouri, Montana, Nevada, New Hampshire, New Jersey, New Mexico, New York, North Dakota, Ohio, Oklahoma, Oregon, Rhode Island, South Dakota, Tennessee, Texas, Utah, Washington, West Virginia, Wisconsin, and Wyoming).
  • Geographic Spread of Influenza Viruses: Widespread influenza activity was reported by 5 states (Connecticut, Delaware, Massachusetts, New York, and Rhode Island). Regional influenza activity was reported by Guam, Puerto Rico and 16 states (Alaska, Arizona, California, Kentucky, Maine, Montana, Nebraska, New Hampshire, New Jersey, North Dakota, Ohio, Pennsylvania, Vermont, Virginia, Washington, and Wisconsin). Local influenza activity was reported by 21 states (Arkansas, Colorado, Florida, Georgia, Idaho, Illinois, Iowa, Kansas, Louisiana, Maryland, Michigan, Minnesota, Missouri, New Mexico, North Carolina, Oklahoma, South Carolina, South Dakota, Utah, West Virginia, and Wyoming). Sporadic influenza activity was reported by the District of Columbia and six states (Hawaii, Indiana, Nevada, Oregon, Tennessee, and Texas). No influenza activity was reported by the U.S. Virgin Islands and two states (Alabama and Mississippi).
  • Flu-Associated Hospitalizations: Since October 1, 2017, 29,629 laboratory-confirmed influenza-associated hospitalizations have been reported through the Influenza Hospitalization Network (FluSurv-NET), a population-based surveillance network for laboratory-confirmed influenza-associated hospitalizations. This translates to a cumulative overall rate of 103.7 hospitalizations per 100,000 people in the United States.
    • The highest hospitalization rate is among people 65 years and older (446.4 per 100,000), followed by adults aged 50-64 years (112.8 per 100,000), and younger children aged 0-4 years (72.7 per 100,000). During most seasons, adults 65 years and older have the highest hospitalization rates, followed by children 0-4 years.
      • The rates reported this season are higher than the end-of-season hospitalization rates for all ages (cumulative) and all age-group specific rates for the 2014-2015 flu season.
    • Hospitalization data are collected from 13 states and represent approximately 9% of the total U.S. population. The number of hospitalizations reported does not reflect the actual total number of influenza-associated hospitalizations in the United States. Additional data, including hospitalization rates during other influenza seasons, can be found at http://gis.cdc.gov/GRASP/Fluview/FluHospRates.html and http://gis.cdc.gov/grasp/fluview/FluHospChars.html.
  • Mortality Surveillance:
    • The proportion of deaths attributed to pneumonia and influenza (P&I) decreased and was 7.1% for the week ending March 31, 2018 (week 13). The percentage is below the epidemic threshold of 7.2% for week 13 in the National Center for Health Statistics (NCHS) Mortality Surveillance System.
    • NCHS data are delayed for two weeks to allow for the collection of enough data to produce stable P&I percentages.
    • Region and state-specific data are available at https://gis.cdc.gov/grasp/fluview/mortality.html.
  • Pediatric Deaths:
    • Five influenza-associated pediatric deaths were reported to CDC during week 15.
      • One death was associated with an influenza A(H3) virus and occurred during week 13 (the week ending March 31, 2018). One death was associated with an influenza A(H1N1)pdm09 virus and occurred during week 6 (the week February 10, 2018). One death was associated with an influenza A virus for which subtyping was not performed and occurred during week 1 (the week ending January 6, 2018).  Two deaths were associated with an influenza B virus and occurred during weeks 9 and 14 (the weeks ending March 3, and April 7, 2018, respectively).
    • A total of 156 influenza-associated pediatric deaths for the 2017-2018 flu season have been reported to CDC.
  • Laboratory Data:
    • Nationally, the percentage of respiratory specimens testing positive for influenza viruses in clinical laboratories during the week ending April 14 was 10.9%.
    • Regionally, the three-week average percent of specimens testing positive for influenza in clinical laboratories ranged from 3.5% to 19.7%.
    • During the week ending April 14, of the 2,056 (10.9%) influenza-positive tests reported to CDC by clinical laboratories, 706 (34.3%) were influenza A viruses and 1,350 (65.7%) were influenza B viruses.
    • Influenza A(H3) viruses have predominated this season. Since early March, influenza B viruses have been more frequently reported than influenza A viruses.
    • During the week ending April 14, 101 (34.8%) of the 290 influenza-positive tests reported to CDC by public health laboratories were influenza A viruses and 189 (65.2%) were influenza B viruses. Of the 99 influenza A viruses that were subtyped, 59 (59.6%) were H3N2 viruses and 40 (40.4%) were (H1N1)pdm09 viruses.
    • The majority of the influenza viruses collected from the United States during October 1, 2017 through April 14, 2018 were characterized antigenically and genetically as being similar to the cell-grown reference viruses representing the 2017–18 Northern Hemisphere influenza vaccine viruses.
    • Since October 1, 2017, CDC has tested 969 influenza A(H1N1)pdm09, 1,955 influenza A(H3N2), and 887 influenza B viruses for resistance to antiviral medications (i.e., oseltamivir, zanamivir, or peramivir). While the majority of the tested viruses showed susceptibility to the antiviral drugs, 10 (1.0%) H1N1pdm09 viruses were resistant to both oseltamivir and peramivir, but were sensitive to zanamivir.

FluView is available – and past issues are archived – on the CDC website.

Note: Delays in reporting may mean that data changes over time. The most up to date data for all weeks during the 2017-2018 season can be found on the current FluView and FluView Interactive.

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